Chemical-mechanical planarization (CMP) processes planarize the surface of semiconductor wafers to a desired thickness. In a typical CMP process, a wafer attached to a carrier is pressed against a polishing pad in the presence of a slurry. The slurry contains abrasive particles that mechanically remove material from the wafer and chemicals that chemically remove material from the wafer. At least one of the carrier or the pad moves with respect to the other to move the wafer over the pad and gradually planarize the wafer to a desired thickness.
After planarizing a number of wafers, the planarizing surface of a pad degrades and becomes less effective. Planarizing surfaces degrade because waste matter, in the form of particles from the wafer, pad and slurry, accumulates on the planarizing surface of the polishing pad during planarization. The waste matter on the pad reduces the effectiveness and the uniformity of the planarizing surface of the polishing pad. The waste matter accordingly reduces throughput of the CMP process and the uniformity of the polished surface on the wafer. Accordingly, it is necessary to periodically clean the planarizing surface of a polishing pad.
Planarizing surfaces of polishing pads are conventionally cleaned by brushing the pad with a stiff brush, or by flushing the pad with a fluid. One problem with brushing the pad is that the bristles of the brush may abrade the pad surface. Moreover, brushes do not effectively remove the dislodged particles from the surface. Flushing the planarizing surface with a fluid does not abrade the pad, but, because high fluid velocities are required to separate the waste matter from the pad, the dislodged particles of waste matter travel along random trajectories and land on previously cleaned portions of the pad's surface.